add a solution for 560

Author: fishercoder1534

src/main/java/com/fishercoder/solutions/_560.java

@@ -32,4 +32,30 @@ public int subarraySum(int[] nums, int k) {
         }
     }
 
+    public static class Solution2 {
+        /**
+         * My completely original solution on 10/14/2021.
+         * Again, using a pen and paper to visualize your thought process just clears out all ambiguities.
+         */
+        public int subarraySum(int[] nums, int k) {
+            int ans = 0;
+            int[] prefixSum = new int[nums.length];
+            prefixSum[0] = nums[0];
+            for (int i = 1; i < nums.length; i++) {
+                prefixSum[i] = prefixSum[i - 1] + nums[i];
+            }
+            for (int i = 0; i < nums.length; i++) {
+                if (prefixSum[i] == k) {
+                    ans++;
+                }
+                for (int j = 0; j < i; j++) {
+                    if (prefixSum[i] - prefixSum[j] == k) {
+                        ans++;
+                    }
+                }
+            }
+            return ans;
+        }
+    }
+
 }

src/test/java/com/fishercoder/_560Test.java

@@ -6,11 +6,9 @@
 
 import static org.junit.Assert.assertEquals;
 
-/**
- * Created by fishercoder on 4/29/17.
- */
 public class _560Test {
     private static _560.Solution1 solution1;
+    private static _560.Solution2 solution2;
     private static int expected;
     private static int actual;
     private static int[] nums;
@@ -19,6 +17,7 @@ public class _560Test {
     @BeforeClass
     public static void setup() {
         solution1 = new _560.Solution1();
+        solution2 = new _560.Solution2();
     }
 
     @Test
@@ -28,5 +27,52 @@ public void test1() {
         expected = 2;
         actual = solution1.subarraySum(nums, k);
         assertEquals(expected, actual);
+        actual = solution2.subarraySum(nums, k);
+        assertEquals(expected, actual);
+    }
+
+    @Test
+    public void test2() {
+        nums = new int[]{1, 2, 3};
+        k = 3;
+        expected = 2;
+        actual = solution1.subarraySum(nums, k);
+        assertEquals(expected, actual);
+        actual = solution2.subarraySum(nums, k);
+        assertEquals(expected, actual);
+    }
+
+    @Test
+    public void test3() {
+        nums = new int[]{1, 1};
+        k = 1;
+        expected = 2;
+        actual = solution1.subarraySum(nums, k);
+        assertEquals(expected, actual);
+        actual = solution2.subarraySum(nums, k);
+        assertEquals(expected, actual);
     }
+
+    @Test
+    public void test4() {
+        nums = new int[]{0, 0};
+        k = 0;
+        expected = 3;
+        actual = solution1.subarraySum(nums, k);
+        assertEquals(expected, actual);
+        actual = solution2.subarraySum(nums, k);
+        assertEquals(expected, actual);
+    }
+
+    @Test
+    public void test5() {
+        nums = new int[]{100, 1, 2, 3, 4};
+        k = 3;
+        expected = 2;
+        actual = solution1.subarraySum(nums, k);
+        assertEquals(expected, actual);
+        actual = solution2.subarraySum(nums, k);
+        assertEquals(expected, actual);
+    }
+
 }